The activation of leukocytes initiates a series of complex events, including the induction of interferons of one or more species (alpha, beta or gamma). These interferons can, in turn, modulate leukocyte activity. Our study will characterize the IFN species produced by leukocyte suspensions of human and murine origin stimulated by virus or mitogen. In addition, the effects of these IFNs in enhancing (priming) IFN synthesis by leukocytes and in suppressing lymphocyte proliferation will be evaluated.